Standardized Electrochemical Characterization of Conductive Hydrogels

Conductive hydrogels are hydrated materials with mixed ionic‐electronic conduction that readily bridge living tissue with electronic devices. As bioelectronic interfaces are underpinned by ionic and electronic conductivity, it is important to carefully characterize both contributions. The soft, hydrated, 3D nature of hydrogels creates a challenge for reproducible conductivity measurements compared to materials with thin-film form factors. Here, we develop a robust method for performing electrochemical impedance spectroscopy (EIS) on conductive hydrogels that is accurate, reproducible, and accessible. The two-electrode system uses a water-tight Swagelok cell with tunable electrode distances. We demonstrate our method using representative PEDOT:PSS-incorporated hydrogels exhibiting varying degrees of ionic and electronic conductivity; simplified equivalent circuits support reliable analysis of electrochemical impedance data. To lower the barrier to entry, we provide a list of materials/suppliers, standard-operating-procedures, and open-source code for fitting the acquired data. Furthermore, we explore common confounding factors to characterization such as ionic strength, storage conditions, and mechanical compression, and offer strategies to reduce batch-to-batch error. This method provides an accessible means to decouple mixed conduction in this class of materials to guide future material design efforts for bioelectronic applications.